Transcript What Happens to Negatively Charged Lipid Vesicles Upon Interacting with Polycation Species?

What happens to negatively charged
lipid vesicles upon interacting with
polycation species?
Ali DURAN
POLYMER TECHNOLOGY
1
INTRODUCTION
 Synthetic polyelectrolytes are widely used now in medicine and
biology, in particular for stimulation of immune response,
 This requires to study the behaviour of polyelectrolytes in
biological environment and especially, their interaction with cells,
 It is known that a cell membrane usually carries a net negative
charge,
 Therefore, this study focused on synthetic polycations interacting
with mixed vesicles composed of neutral phosphatidylcholine and
diphosphatidylglycerol (cardilipin, CL2- ) carrying two negative
headgroups,
2
RESULTS AND DISCUSSION
 It was found that binding of both CP(2)
and CP(2,16) to solid and liquid DPPCCL2- vesicles accompanied by
neutralization of the liposome surface
charge, registered by measuring EPM of
polycation-vesicle complexes,
 As follows from the figures, the largest
particle size was observed at EPM=0,
 Further increase in polycation
concentration resulted in overcharging
of the complex species and a decrease
in particle size,
 In this polycation concentration range,
the complex species were stabilized
against aggregation by the abundant
positive charge of the adsorbed
3
polycation,
RESULTS AND DISCUSSION
 The cardinal difference in the behavior
of solid and liquid vesicles revealed in
the amount of negative CL2- molecules
formed salt bonds with the polycation
units.
 As expected, in the case of the solid
vesicles, the neutralizing amount of the
polycation, measured at EPM=0, was
equal to a half amount of CL2- involved
in the vesicular membranes,
 However, in the case of liquid
liposomes, the EPM=0 point
corresponded to the total amount of
the membrane CL2- ,
4
RESULTS AND DISCUSSION
 In addition, polycation adsorption
induced lateral lipid segregation in the
DPPC-CL membrane revealed in
increase in the bilayer melting point
and sharpening of DSC curves,
 As a result, the initial membrane
divided into two two-dimensional
microphases: one composed of neutral
DPPC molecules, and other of CL
molecules kept together due to ionic
contacts of their negative headgroups
with positive polycation units,
5
RESULTS AND DISCUSSION
 In other words, polycation
adsorption on negativelycharged liquid vesicles led to a
sharp charge asymmetry in the
vesicular membrane,
6
RESULTS AND DISCUSSION
 However, the liquid vesicles
retained their integrity when
adsorbed CP(2) unless V
exceeded a certain critical value,
 At higher V values, polycation
adsorption resulted in irreversible
vesicle disruption indicated by a
sharp conductivity increase in the
systems containing the vesicles
filled with NaCl,
7
Adsorption of polycations on the surface of the labeled EL-CL2- vesicles
resulted in quenching of FITC fluorosence. It was found that CP(2) could
be completely removed from the surface of liquid EL-CL2- vesicles either
by recomplexation with an excess of PAA or by addition of an excess of a
simple salt.
8
CONCLUSIONS
 It was found that the negative 3:1 PAA-CP(2,16) complex bound
to negative vesicles as a whole,
 Therefore, complexation with hydrophobized polycation can be
used to enhance the affinity of negative biologically active
macromolecules to biomembranes,
 Interaction of polycations with vesicles depending on their
composition, phase state of the lipid bilayer and chemical
structure of a polycation can be accompanied by lateral lipid
segregation, highly accelerated transmembrane migration of lipid
molecules, incorporation of adsorbed polycations into vesicular
membrane as well as aggregation and disruption of vesicles,
9
CONCLUSIONS
 The electrostatically adsorbed polycation, CP(2), can be completely
removed from the liquid vesicle membrane by an increase in simple
salt concentration or by recomplexation with polyanions,
 This results in resumption of the initial lateral and transmembrane
lipid distribution in vesicle bilayer,
 In contrast, complexation of polycation carrying hydrophobes,
CP(2,16), with negative vesicular membranes is controlled by both
electrostatic and hydrophobic interactions,
 Such polycations retain contact to the vesicles even in concentrated
salt solutions and in the presence of competing polyions apparently
due to incorporation of hydrophobic polycation fragments into the
hydrophobic part of the membrane.
10
THANKS FOR
YOUR
ATTENTION...
11